1. Field of the Invention
The present invention relates to a glass precision valve for use in combination with liquid measuring instruments, and methods for making the same, wherein the valve means is a unit including a valve body and a valve seat adapted to allow the valve body to slide thereon. As its name implies, the glass precision valve must be especially watertight so as to keep the testing or measuring liquid pure or fresh.
2. Description of the Prior Art
In order to fully describe the background of the invention, reference will be made to FIGS. 16 to 20:
A liquid specimen is often observed through a transparent receptacle, in which the specimen is watertightly contained. The common practice is illustrated in its simplest form in FIG. 16. The reference numeral 1 denotes a glass tubular receptacle which has check valves 2 and 3 at the inlet and the outlet, respectively. The specimen 4 flows from the inlet to the outlet through the two check valves 2, 3. In this example, the check valves 2, 3 must be carefully constructed so as not to cause a leakage.
For such use there are many types of precision valves available in the market, but they are not satisfactory because of the following disadvantages:
1. The example shown in FIG. 17 uses an electromagnet for moving a valve body 5 in a space 6. Many valve bodies are made of elastic substance, such as rubber. Because of the elastic body of the valve the capacity of the space varies. Another disadvantage is that a source of power is required for operating the valve 5.
2. The example shown in FIG. 18 uses a glass valve 7, which moves in a glass receptacle. Because of the glass construction of the two members they keep watertight contact with each other, but when the rotary valve body 7 is to be smoothly rotated, it will be required to apply a lubricant 8, such as silicone grease, interfacially. The use of a lubricant is likely to contaminate the specimen when it is introduced in the receptacle.
3. The example shown in FIG. 19 uses a valve 12 made of other material than metal. To produce a confined space the common practice is to connect between a glass tube 11 and a valve tube 13 by means of an elastic tube 10. Here a gap 14 is disadvantageously produced, which varies the capacity of the confined space. In addition, the specimen is in danger of contamination with the previously used liquid.
4. The example shown in FIG. 20 uses an O-ring 15 for a sealer. However, this also leads to the detrimental variation of the capacity of the confined space. Even when the variation is slight, it will not be negligible when the capacity is small. In addition, the O-rings and the valve seat are in contact on points, and a foreign matter is likely to gather, thereby hampering the smooth movement of the valve body.
Referring to FIGS. 3 and 6, the conventional method of producing a glass precision valve will be described:
A drill 16 having a conically sharpened head is rotated at a high speed, wherein the head is coated with diamond powder. In FIGS. 3 and 4, the rotating drill 16 is approached to the glass rod 17 which is also rotated at a high speed. Likewise, the rotating, drill 16 is caused to enter a valve casing having a rotating glass bulged portion 20 until it comes into contact with the bottom thereof. The bulged portion 20 has a glass tube 18. As shown in FIG. 6, the drill 16 grinds the inside surface of the glass tube 18, thereby producing a valve seat 22. The valve body 21 is produced from the glass rod 17 as mentioned above. The finished valve body and seat are mutually rubbed with the use of fine diamond powder 23 interfacially placed therebetween, so as to enhance the liquid-tightness therebetween. The degree of the liquid-tightness is controlled by the grain size of the diamond powder used at the final stage. FIGS. 7 and 8 illustrates this operation.
This conventional practice is commonly called a grinding method, and it is widely used. However, this practice causes the above-mentioned drawbacks, particularly the problem of contamination. A further disadvantage is that the valve body tends to stick to the valve seat through repeated use, thereby reducing the working efficiency.